Prefer const in test files (#1117)

* Removed all instances of var.

* Sorted eslintrc rules.

* Made eslint rule severity explicit.

* Now prefering const over let.

test/helpers/sendTransaction.js

@@ -2,7 +2,7 @@ const _ = require('lodash');
 const ethjsABI = require('ethjs-abi');
 
 function findMethod (abi, name, args) {
-  for (var i = 0; i < abi.length; i++) {
+  for (let i = 0; i < abi.length; i++) {
     const methodArgs = _.map(abi[i].inputs, 'type').join(',');
     if ((abi[i].name === name) && (methodArgs === args)) {
       return abi[i];